Implantable medical devices are well known in the art for treating a variety of medical conditions. These may be, for instance, stents, stent grafts, vascular filters, vascular occluders, as well as prosthetic elements such as supplemental or replacement valve elements and so on. It is important for such implantable medical devices to be deployed in a vessel in a manner that they seal properly with the vessel wall and that they retain a good seal over time. While this is possible with many designs of implantable medical device, some devices have shapes and structures which can tilt within the vessel, potentially leading to loss of sealing to the vessel wall and possible migration of the device. The risk of tilting is notable with devices such as vascular filters and occluders, which tend to have non-cylindrical structures, particularly being conical in shape. It is common for such devices to include elements intended to maintain the filter or occluder properly aligned in the vessel, although such measures do not necessarily achieve their intended function. In some cases it is also desirable to have a plurality of device units arranged in series, for instance a series of filtering elements, for optimising the performance characteristics of the device. A structure of such a type is longer than a single unit and it is not unusual for a multi-unit structure device to be deployed in a curved vessel, leading to considerations of proper orientation of each unit within the vessel.
Examples of known vascular filter assemblies are disclosed in US-2008/0275490, US-2013/0345739, US-2013/0238010, US-2011/0251629, U.S. Pat. Nos. 8,486,105 and 8,252,018.